a(n) = n! * [x^n] exp(n*x)/cos(x).

Terms

a(0) =1a(1) =1a(2) =5a(3) =36a(4) =357a(5) =4500a(6) =68857a(7) =1239504a(8) =25661545a(9) =600655824a(10) =15684383021a(11) =452001644864